Composite trusses having wood chords and metal webs have been in commerical use for about 16 years. Builders have avoided hanging composite trusses by the top chord members flush with or below the supporting plate member because the custom made hangers were too heavy, too expensive and difficult to install.
Truss fabricators were unable to find a simple solution and resorted to heavily reinforced custom-modified simple joist hangers. Use of redesigned standard joist hangers was, however, not a good solution since the forces acting on a hanger from a simple beam are entirely different from the forces acting on the ends of a truss. Hangers for simple beams merely require a device which transmits supporting load from a bearing member through a strap of "U" element which encapsulates and supports the end of the beam or joist. Usually, the main support is a simple seat area underneath the edge-end of the joist or beam.
The truss, on the other hand presents a different combination of problems and required load bearing functions. The problem is to provide support not only for the end of the upper chord wood members, but also provide support for the end of the terminal metal web which is located at some distance from the end of the upper chord, thus imposing a rotational load in respect to bearing.
Since building walls are seldom constructed to the tolerances required in the fabrication of trusses, a hanger, to be successful commercially must have an adjustability to accommodate the trusses within the tolerance allowable in constructing the building walls.
The current state of the art is to provide a more or less conventional hanger of a size and mass primarily governed by its ability to resist the eccentric arm of loading rather than being governed by the simple load bearing requirements. Into and upon the seat of such a hanger, is normally placed a double-angled clip device designed to pick up the transverse bolt which connects through the chord and provides the end support and connection for the end of the terminal web. Sometimes the lower legs of such a clip are slotted to provide adjustment in respect to the hanger seat. Basically, this clip is the same device as used when the top chord of a truss is installed in simple over-the-top bearing relationship to a support. As previously stated, this combination of required hardware is so excessive in relation to a hangered function for trusses as to practically discourage the use of hangered trusses whenever possible.